System and method of testing humidity in a sealed MEMS device

ABSTRACT

One embodiment provides a method of testing humidity. The method includes measuring i) a first weight of a first device which encloses a plurality of interferometric modulators and ii) a second weight of a second device which encloses a plurality of interferometric modulators, wherein the first and second devices contain a different amount of water vapor. The method further includes comparing the weights of the first and second devices and determining a relative humidity value or a degree of the relative humidity inside one of the two devices based at least in part upon the weight comparison. In one embodiment, the relative humidity value or degree is determined considering at least one of the following parameters: i) temperature-humidity combination inside at least one of the devices, ii) the thickness and width of a seal of the at least one device, iii) adhesive permeability of a component of the at least one device, iv) a desiccant capacity inside the at least one device and v) a device size.

RELATED APPLICATIONS

This application is a divisional of and claims priority from U.S.application Ser. No. 11/173,822, filed Jul. 1, 2005, under 35 U.S.C. §120, which is hereby incorporated by reference. U.S. application Ser.No. 11/173,822 also claimed priority under 35 U.S.C. § 119(e) fromprovisional application No. 60/613,567 filed Sep. 27, 2004, which ishereby incorporated by reference.

BACKGROUND

1. Field of the Invention

The field of the invention relates to microelectromechanical systems(MEMS).

2. Description of the Related Technology

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. As used herein, theterm interferometric modulator or interferometric light modulator refersto a device that selectively absorbs and/or reflects light using theprinciples of optical interference. In certain embodiments, aninterferometric modulator may comprise a pair of conductive plates, oneor both of which may be transparent and/or reflective in whole or partand capable of relative motion upon application of an appropriateelectrical signal. In a particular embodiment, one plate may comprise astationary layer deposited on a substrate and the other plate maycomprise a metallic membrane separated from the stationary layer by anair gap. As described herein in more detail, the position of one platein relation to another can change the optical interference of lightincident on the interferometric modulator. Such devices have a widerange of applications, and it would be beneficial in the art to utilizeand/or modify the characteristics of these types of devices so thattheir features can be exploited in improving existing products andcreating new products that have not yet been developed.

Furthermore, in the prior art, it was not recognized that there has beena need to check or measure the level of humidity (relative humidity)inside an MEMS device after the MEMS package fabrication is complete soas to, for example, evaluate the lifetime of the device or determinewhether the package is defective or not.

SUMMARY OF CERTAIN EMBODIMENTS

The system, method, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention, its moreprominent features will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description of Certain Embodiments” one will understand howthe features of this invention provide advantages over other displaydevices.

One embodiment provides a method of testing humidity. The methodcomprises determining a property of a device which encloses a pluralityof interferometric modulators, and determining a relative humidity valueor a degree of the relative humidity inside the device based at least inpart upon the determined property.

Another embodiment provides a system for testing humidity. The systemcomprises means for determining a property of a device which encloses aplurality of interferometric modulators, and means for determining arelative humidity value or a degree of the relative humidity inside thedevice based at least in part upon the determined property.

Another embodiment provides a method of testing humidity. The methodcomprises measuring i) a first weight of a first device which encloses aplurality of interferometric modulators and ii) a second weight of asecond device which encloses a plurality of interferometric modulators,wherein the first and second devices contain a different amount of watervapor. The method also comprises comparing the weights of the first andsecond devices, and determining a relative humidity value or a degree ofthe relative humidity inside one of the two devices based at least inpart upon the weight comparison.

Another embodiment provides a system for testing humidity. The systemcomprises a first device enclosing a plurality of interferometricmodulators, and a second device enclosing a plurality of interferometricmodulators, wherein the first and second devices contain a differentamount of water vapor. The system also comprises a scale configured tomeasure the weights of the first and second devices, wherein a relativehumidity value or a degree of the relative humidity inside one of thetwo devices is determined based at least in part upon the measuredweights.

Another embodiment provides a method of testing humidity. The methodcomprises measuring i) a weight of a device which encloses a pluralityof interferometric modulators and ii) an average weight of a pluralityof devices each enclosing a plurality of interferometric modulators,wherein at least one of the plurality of devices contains a differentamount of water vapor from that of the device. The method also comprisescomparing the weight of the device with the average weight; anddetermining a relative humidity value or a degree of the relativehumidity inside the device based at least in part upon the weightcomparison.

Another embodiment provides a method of testing humidity. The methodcomprises providing a device which encloses i) a plurality ofinterferometric modulators and ii) a desiccant, wherein the desiccant isconfigured to change its color based on an amount of water vaporabsorbed therein. The method also comprises determining a degree of acolor change of the desiccant, and determining a relative humidity valueor a degree of the relative humidity inside the device based at least inpart upon the determined degree of the color change.

Another embodiment provides a method of manufacturing amicroelectromechanical systems (MEMS) device. The method comprisesproviding a substrate, forming a plurality of interferometric modulatorson the substrate, providing a desiccant configured to change its colorbased on an amount of water vapor absorbed therein, and providing abackplate. The method also comprises joining the substrate and thebackplate so as to form a device which encloses the plurality ofinterferometric modulators and the desiccant, wherein the backplateincludes at least one transparent portion through which the color changeof the desiccant can be viewed from the outside of the device.

Another embodiment provides a microelectromechanical systems (MEMS)device. The system comprises a substrate, a plurality of interferometricmodulators formed on the substrate; a desiccant configured to change itscolor based on an amount of water vapor absorbed therein, and abackplate. The substrate and backplate are joined to each other so as toform a device which encloses the plurality of interferometric modulatorsand the desiccant, wherein the backplate includes at least onetransparent portion through which the color change of the desiccant canbe viewed from the outside of the device.

Another embodiment provides a method of testing humidity. The methodcomprises providing a device which encloses a plurality ofinterferometric modulators, measuring a resistance of at least oneinterior part of the device, and determining a relative humidity valueor a degree of the relative humidity inside the device based at least inpart upon the measured resistance.

Another embodiment provides a system for testing humidity. The systemcomprises a device enclosing a plurality of interferometric modulators,and a resistive sensor configured to measure a resistance of at leastone interior part of the device, wherein a relative humidity value or adegree of the relative humidity inside the device is determined based atleast in part upon the measured resistance.

Another embodiment provides a method of testing humidity. The methodcomprises i) providing a device which encloses a plurality ofinterferometric modulators, ii) operably contacting an outside area ofthe device with a cold finger device, set at a first temperature, iii)determining whether frost forms in an inside area of the interferometricmodulator device to the contacted area, and iv) determining a relativehumidity value or a degree of the relative humidity inside theinterferometric modulator device based at least in part upon whetherfrost has formed in the inside area.

Another embodiment provides a system for testing humidity. The systemcomprises a device enclosing a plurality of interferometric modulators,and a cold finger device configured to make an operable contact with anoutside area of the device. A relative humidity value or a degree of therelative humidity inside the interferometric modulator device isdetermined based at least in part upon whether frost has formed in theinside area.

Still another embodiment provides a method of testing humidity. Themethod comprises providing a device which encloses a plurality ofinterferometric modulators, and operably contacting an outside area ofthe device with a cold finger device. The method also comprisesdetermining whether frost forms in an inside area of the interferometricmodulator device corresponding to the contacted area, and measuring aresistance of at least one interior part of the interferometricmodulator device. The method further comprises determining a relativehumidity value or a degree of the relative humidity inside theinterferometric modulator device based at least in part upon thecombination of i) whether frost has formed in the inside area and ii)the measured resistance.

Still another embodiment provides a system for testing humidity. Thesystem comprises i) a device enclosing a plurality of interferometricmodulators, ii) a cold finger device configured to make an operablecontact with an outside area of the interferometric modulator device,and iii) a resistive sensor configured to measure a resistance of atleast one interior part of the interferometric modulator device. Arelative humidity value or a degree of the relative humidity inside theinterferometric modulator device is determined based at least in partupon the combination of i) whether frost has formed in the inside areaand ii) the measured resistance.

Yet another embodiment provides a method of testing humidity. The methodcomprises providing a device which encloses a plurality ofinterferometric modulators, and measuring a first weight of the device.The method also comprises measuring a second weight of the device aftera predetermined period of time, and comparing the first and secondweights, and determining a relative humidity value or a degree of therelative humidity inside the device based at least in part upon theweight comparison.

Yet another embodiment provides a method of testing humidity. The methodcomprises providing a device which encloses i) a plurality ofinterferometric modulators and ii) a desiccant, measuring a first weightof the device, and providing water vapor into the inside of the device.The method also comprises measuring a second weight of the device afterthe water vapor has been provided into the device, comparing the firstand second weights, and determining a degree of the relative humidityinside the device based at least in part upon the weight comparison.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a relaxed position and a movablereflective layer of a second interferometric modulator is in an actuatedposition.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltagefor one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIGS. 5A and 5B illustrate one exemplary timing diagram for row andcolumn signals that may be used to write a frame of display data to the3×3 interferometric modulator display of FIG. 2.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa visual display device comprising a plurality of interferometricmodulators.

FIG. 7A is a cross section of the device of FIG. 1.

FIG. 7B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 7C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 7D is a cross section of yet another alternative embodiment of aninterferometric modulator.

FIG. 7E is a cross section of an additional alternative embodiment of aninterferometric modulator.

FIG. 8 is a conceptual diagram showing a process of humidity testing inthe inside of the package according to embodiments of the invention.

FIGS. 9A and 9B illustrate a humidity testing process according to oneembodiment of the invention.

FIG. 9C illustrates a humidity testing process according to oneembodiment of the invention.

FIGS. 10A-10C illustrate a humidity testing process according to anotherembodiment of the invention.

FIG. 10D illustrates a humidity testing process according to anotherembodiment of the invention.

FIGS. 11A and 11B illustrate a humidity testing process according toanother embodiment of the invention.

FIGS. 12A-12C illustrate a humidity testing process according to stillanother embodiment of the invention.

FIG. 13 illustrates a humidity testing process according to yet anotherembodiment of the invention.

FIG. 14 illustrates an exemplary flowchart for explaining a humiditytesting process according to embodiments of the invention.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout. As will be apparent from the following description, theembodiments may be implemented in any device that is configured todisplay an image, whether in motion (e.g., video) or stationary (e.g.,still image), and whether textual or pictorial. More particularly, it iscontemplated that the embodiments may be implemented in or associatedwith a variety of electronic devices such as, but not limited to, mobiletelephones, wireless devices, personal data assistants (PDAs), hand-heldor portable computers, GPS receivers/navigators, cameras, MP3 players,camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, computer monitors, autodisplays (e.g., odometer display, etc.), cockpit controls and/ordisplays, display of camera views (e.g., display of a rear view camerain a vehicle), electronic photographs, electronic billboards or signs,projectors, architectural structures, packaging, and aestheticstructures (e.g., display of images on a piece of jewelry). MEMS devicesof similar structure to those described herein can also be used innon-display applications such as in electronic switching devices.

One embodiment provides a method of testing humidity, which comprises i)exposing a device which encloses a plurality of interferometricmodulators to a humid environment, ii) determining a property (weight,resistance, desiccant color change, temperature where frost forms, etc.)and iii) determining a relative humidity value or a degree of therelative humidity inside the device based at least in part upon thedetermined property.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical cavity with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as therelaxed position, the movable reflective layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, referred to herein as the actuated position, themovable reflective layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable reflective layer 14 a isillustrated in a relaxed position at a predetermined distance from anoptical stack 16 a, which includes a partially reflective layer. In theinterferometric modulator 12 b on the right, the movable reflectivelayer 14 b is illustrated in an actuated position adjacent to theoptical stack 16 b.

The optical stacks 16 a and 16 b (collectively referred to as opticalstack 16), as referenced herein, typically comprise of several fusedlayers, which can include an electrode layer, such as indium tin oxide(ITO), a partially reflective layer, such as chromium, and a transparentdielectric. The optical stack 16 is thus electrically conductive,partially transparent and partially reflective, and may be fabricated,for example, by depositing one or more of the above layers onto atransparent substrate 20. In some embodiments, the layers are patternedinto parallel strips, and may form row electrodes in a display device asdescribed further below. The movable reflective layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes of 16 a, 16 b) deposited on topof posts 18 and an intervening sacrificial material deposited betweenthe posts 18. When the sacrificial material is etched away, the movablereflective layers 14 a, 14 b are separated from the optical stacks 16 a,16 b by a defined gap 19. A highly conductive and reflective materialsuch as aluminum may be used for the reflective layers 14, and thesestrips may form column electrodes in a display device.

With no applied voltage, the cavity 19 remains between the movablereflective layer 14 a and optical stack 16 a, with the movablereflective layer 14 a in a mechanically relaxed state, as illustrated bythe pixel 12 a in FIG. 1. However, when a potential difference isapplied to a selected row and column, the capacitor formed at theintersection of the row and column electrodes at the corresponding pixelbecomes charged, and electrostatic forces pull the electrodes together.If the voltage is high enough, the movable reflective layer 14 isdeformed and is forced against the optical stack 16. A dielectric layer(not illustrated in this Figure) within the optical stack 16 may preventshorting and control the separation distance between layers 14 and 16,as illustrated by pixel 12 b on the right in FIG. 1. The behavior is thesame regardless of the polarity of the applied potential difference. Inthis way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2 through 5 illustrate one exemplary process and system for usingan array of interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device that may incorporate aspects of the invention. In theexemplary embodiment, the electronic device includes a processor 21which may be any general purpose single- or multi-chip microprocessorsuch as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®,Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any specialpurpose microprocessor such as a digital signal processor,microcontroller, or a programmable gate array. As is conventional in theart, the processor 21 may be configured to execute one or more softwaremodules. In addition to executing an operating system, the processor maybe configured to execute one or more software applications, including aweb browser, a telephone application, an email program, or any othersoftware application.

In one embodiment, the processor 21 is also configured to communicatewith an array driver 22. In one embodiment, the array driver 22 includesa row driver circuit 24 and a column driver circuit 26 that providesignals to a display array or panel 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. For MEMSinterferometric modulators, the row/column actuation protocol may takeadvantage of a hysteresis property of these devices illustrated in FIG.3. It may require, for example, a 10 volt potential difference to causea movable layer to deform from the relaxed state to the actuated state.However, when the voltage is reduced from that value, the movable layermaintains its state as the voltage drops back below 10 volts. In theexemplary embodiment of FIG. 3, the movable layer does not relaxcompletely until the voltage drops below 2 volts. There is thus a rangeof voltage, about 3 to 7 V in the example illustrated in FIG. 3, wherethere exists a window of applied voltage within which the device isstable in either the relaxed or actuated state. This is referred toherein as the “hysteresis window” or “stability window.” For a displayarray having the hysteresis characteristics of FIG. 3, the row/columnactuation protocol can be designed such that during row strobing, pixelsin the strobed row that are to be actuated are exposed to a voltagedifference of about 10 volts, and pixels that are to be relaxed areexposed to a voltage difference of close to zero volts. After thestrobe, the pixels are exposed to a steady state voltage difference ofabout 5 volts such that they remain in whatever state the row strobe putthem in. After being written, each pixel sees a potential differencewithin the “stability window” of 3-7 volts in this example. This featuremakes the pixel design illustrated in FIG. 1 stable under the sameapplied voltage conditions in either an actuated or relaxed pre-existingstate. Since each pixel of the interferometric modulator, whether in theactuated or relaxed state, is essentially a capacitor formed by thefixed and moving reflective layers, this stable state can be held at avoltage within the hysteresis window with almost no power dissipation.Essentially no current flows into the pixel if the applied potential isfixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4 and 5 illustrate one possible actuation protocol for creating adisplay frame on the 3×3 array of FIG. 2. FIG. 4 illustrates a possibleset of column and row voltage levels that may be used for pixelsexhibiting the hysteresis curves of FIG. 3. In the FIG. 4 embodiment,actuating a pixel involves setting the appropriate column to −V_(bias),and the appropriate row to +ΔV, which may correspond to −5 volts and +5volts respectively Relaxing the pixel is accomplished by setting theappropriate column to +V_(bias), and the appropriate row to the same+ΔV, producing a zero volt potential difference across the pixel. Inthose rows where the row voltage is held at zero volts, the pixels arestable in whatever state they were originally in, regardless of whetherthe column is at +V_(bias), or −V_(bias+). As is also illustrated inFIG. 4, it will be appreciated that voltages of opposite polarity thanthose described above can be used, e.g., actuating a pixel can involvesetting the appropriate column to +V_(bias), and the appropriate row to−ΔV. In this embodiment, releasing the pixel is accomplished by settingthe appropriate column to −V_(bias), and the appropriate row to the same−ΔV, producing a zero volt potential difference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or relaxed states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and relaxes the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thesystems and methods described herein.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa display device 40. The display device 40 can be, for example, acellular or mobile telephone. However, the same components of displaydevice 40 or slight variations thereof are also illustrative of varioustypes of display devices such as televisions and portable media players.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 44, an input device 48, and a microphone 46. The housing41 is generally formed from any of a variety of manufacturing processesas are well known to those of skill in the art, including injectionmolding, and vacuum forming. In addition, the housing 41 may be madefrom any of a variety of materials, including but not limited toplastic, metal, glass, rubber, and ceramic, or a combination thereof. Inone embodiment the housing 41 includes removable portions (not shown)that may be interchanged with other removable portions of differentcolor, or containing different logos, pictures, or symbols.

The display 30 of exemplary display device 40 may be any of a variety ofdisplays, including a bi-stable display, as described herein. In otherembodiments, the display 30 includes a flat-panel display, such asplasma, EL, OLED, STN LCD, or TFT LCD as described above, or anon-flat-panel display, such as a CRT or other tube device, as is wellknown to those of skill in the art. However, for purposes of describingthe present embodiment, the display 30 includes an interferometricmodulator display, as described herein.

The components of one embodiment of exemplary display device 40 areschematically illustrated in FIG. 6B. The illustrated exemplary displaydevice 40 includes a housing 41 and can include additional components atleast partially enclosed therein. For example, in one embodiment, theexemplary display device 40 includes a network interface 27 thatincludes an antenna 43 which is coupled to a transceiver 47. Thetransceiver 47 is connected to a processor 21, which is connected toconditioning hardware 52. The conditioning hardware 52 may be configuredto condition a signal (e.g. filter a signal). The conditioning hardware52 is connected to a speaker 45 and a microphone 46. The processor 21 isalso connected to an input device 48 and a driver controller 29. Thedriver controller 29 is coupled to a frame buffer 28, and to an arraydriver 22, which in turn is coupled to a display array 30. A powersupply 50 provides power to all components as required by the particularexemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the exemplary display device 40 can communicate with one or moredevices over a network. In one embodiment the network interface 27 mayalso have some processing capabilities to relieve requirements of theprocessor 21. The antenna 43 is any antenna known to those of skill inthe art for transmitting and receiving signals. In one embodiment, theantenna transmits and receives RF signals according to the IEEE 802.11standard, including IEEE 802.11(a), (b), or (g). In another embodiment,the antenna transmits and receives RF signals according to the BLUETOOTHstandard. In the case of a cellular telephone, the antenna is designedto receive CDMA, GSM, AMPS or other known signals that are used tocommunicate within a wireless cell phone network. The transceiver 47pre-processes the signals received from the antenna 43 so that they maybe received by and further manipulated by the processor 21. Thetransceiver 47 also processes signals received from the processor 21 sothat they may be transmitted from the exemplary display device 40 viathe antenna 43.

In an alternative embodiment, the transceiver 47 can be replaced by areceiver. In yet another alternative embodiment, network interface 27can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. For example, the image source canbe a digital video disc (DVD) or a hard-disc drive that contains imagedata, or a software module that generates image data.

Processor 21 generally controls the overall operation of the exemplarydisplay device 40. The processor 21 receives data, such as compressedimage data from the network interface 27 or an image source, andprocesses the data into raw image data or into a format that is readilyprocessed into raw image data. The processor 21 then sends the processeddata to the driver controller 29 or to frame buffer 28 for storage. Rawdata typically refers to the information that identifies the imagecharacteristics at each location within an image. For example, suchimage characteristics can include color, saturation, and gray-scalelevel.

In one embodiment, the processor 21 includes a microcontroller, CPU, orlogic unit to control operation of the exemplary display device 40.Conditioning hardware 52 generally includes amplifiers and filters fortransmitting signals to the speaker 45, and for receiving signals fromthe microphone 46. Conditioning hardware 52 may be discrete componentswithin the exemplary display device 40, or may be incorporated withinthe processor 21 or other components.

The driver controller 29 takes the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and reformats the raw image data appropriately for high speedtransmission to the array driver 22. Specifically, the driver controller29 reformats the raw image data into a data flow having a raster-likeformat, such that it has a time order suitable for scanning across thedisplay array 30. Then the driver controller 29 sends the formattedinformation to the array driver 22. Although a driver controller 29,such as a LCD controller, is often associated with the system processor21 as a stand-alone Integrated Circuit (IC), such controllers may beimplemented in many ways. They may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

Typically, the array driver 22 receives the formatted information fromthe driver controller 29 and reformats the video data into a parallelset of waveforms that are applied many times per second to the hundredsand sometimes thousands of leads coming from the display's x-y matrix ofpixels.

In one embodiment, the driver controller 29, array driver 22, anddisplay array 30 are appropriate for any of the types of displaysdescribed herein. For example, in one embodiment, driver controller 29is a conventional display controller or a bi-stable display controller(e.g., an interferometric modulator controller). In another embodiment,array driver 22 is a conventional driver or a bi-stable display driver(e.g., an interferometric modulator display). In one embodiment, adriver controller 29 is integrated with the array driver 22. Such anembodiment is common in highly integrated systems such as cellularphones, watches, and other small area displays. In yet anotherembodiment, display array 30 is a typical display array or a bi-stabledisplay array (e.g., a display including an array of interferometricmodulators).

The input device 48 allows a user to control the operation of theexemplary display device 40. In one embodiment, input device 48 includesa keypad, such as a QWERTY keyboard or a telephone keypad, a button, aswitch, a touch-sensitive screen, a pressure- or heat-sensitivemembrane. In one embodiment, the microphone 46 is an input device forthe exemplary display device 40. When the microphone 46 is used to inputdata to the device, voice commands may be provided by a user forcontrolling operations of the exemplary display device 40.

Power supply 50 can include a variety of energy storage devices as arewell known in the art. For example, in one embodiment, power supply 50is a rechargeable battery, such as a nickel-cadmium battery or a lithiumion battery. In another embodiment, power supply 50 is a renewableenergy source, a capacitor, or a solar cell, including a plastic solarcell, and solar-cell paint. In another embodiment, power supply 50 isconfigured to receive power from a wall outlet.

In some implementations control programmability resides, as describedabove, in a driver controller which can be located in several places inthe electronic display system. In some cases control programmabilityresides in the array driver 22. Those of skill in the art will recognizethat the above-described optimization may be implemented in any numberof hardware and/or software components and in various configurations.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 7A-7E illustrate five different embodiments of themovable reflective layer 14 and its supporting structures. FIG. 7A is across section of the embodiment of FIG. 1, where a strip of metalmaterial 14 is deposited on orthogonally extending supports 18. In FIG.7B, the moveable reflective layer 14 is attached to supports at thecorners only, on tethers 32. In FIG. 7C, the moveable reflective layer14 is suspended from a deformable layer 34, which may comprise aflexible metal. The deformable layer 34 connects, directly orindirectly, to the substrate 20 around the perimeter of the deformablelayer 34. These connections are herein referred to as support posts. Theembodiment illustrated in FIG. 7D has support post plugs 42 upon whichthe deformable layer 34 rests. The movable reflective layer 14 remainssuspended over the cavity, as in FIGS. 7A-7C, but the deformable layer34 does not form the support posts by filling holes between thedeformable layer 34 and the optical stack 16. Rather, the support postsare formed of a planarization material, which is used to form supportpost plugs 42. The embodiment illustrated in FIG. 7E is based on theembodiment shown in FIG. 7D, but may also be adapted to work with any ofthe embodiments illustrated in FIGS. 7A-7C as well as additionalembodiments not shown. In the embodiment shown in FIG. 7E, an extralayer of metal or other conductive material has been used to form a busstructure 44. This allows signal routing along the back of theinterferometric modulators, eliminating a number of electrodes that mayotherwise have had to be formed on the substrate 20.

In embodiments such as those shown in FIG. 7, the interferometricmodulators function as direct-view devices, in which images are viewedfrom the front side of the transparent substrate 20, the side oppositeto that upon which the modulator is arranged. In these embodiments, thereflective layer 14 optically shields the portions of theinterferometric modulator on the side of the reflective layer oppositethe substrate 20, including the deformable layer 34. This allows theshielded areas to be configured and operated upon without negativelyaffecting the image quality. Such shielding allows the bus structure 44in FIG. 7E, which provides the ability to separate the opticalproperties of the modulator from the electromechanical properties of themodulator, such as addressing and the movements that result from thataddressing. This separable modulator architecture allows the structuraldesign and materials used for the electromechanical aspects and theoptical aspects of the modulator to be selected and to functionindependently of each other. Moreover, the embodiments shown in FIGS.7C-7E have additional benefits deriving from the decoupling of theoptical properties of the reflective layer 14 from its mechanicalproperties, which are carried out by the deformable layer 34. Thisallows the structural design and materials used for the reflective layer14 to be optimized with respect to the optical properties, and thestructural design and materials used for the deformable layer 34 to beoptimized with respect to desired mechanical properties.

Generally, interferometric modulators have a higher tolerance forhumidity requirements than that of OLED devices. As discussed above, itis possible that water vapor permeates into the package even if it issemi-hermetically or hermetically sealed. In certain embodiments where adesiccant is placed in the interior of the package, a certain amount ofmoisture permeation may be tolerated depending on the capacity of thedesiccant. However, if there exists moisture or water vapor which ishigher than the tolerance level, or more water permeation into thepackage than desired, the interferometric modulator display device islikely to have a shortened lifetime or may fail to properly operate.Also, in certain packages, moisture, which has been created and/orpermeated during the assembly, may not have been properly removed beforecompleting the fabrication of the package. Furthermore, the relativehumidity level in the interior of the package, particularly, without adesiccant therein, should be maintained less than a certain level inorder that the device operates for its intended purpose or to have anexpected lifetime. Thus, there has been a need to check or measure thelevel of humidity (relative humidity) inside the package after thepackage fabrication is complete so as to, for example, evaluate thelifetime of the device or determine whether the package is defective ornot.

FIG. 8 illustrates a conceptual diagram showing a process of humiditytesting in the inside of the package according to embodiments of theinvention. FIG. 14 illustrates an exemplary flowchart for explaining ahumidity testing process according to embodiments of the invention.Referring to FIGS. 8-14, the humidity testing procedure of variousembodiments will be described in more detail.

First, a fabricated package 51 for humidity testing is sampled(selected) (200). As shown in FIG. 8, the fabricated package 51 includesa substrate 100 and a backplate 80. An interferometric modulator array54, including a plurality of interferometric modulators, is encapsulatedwithin the package 51. The substrate 100 and backplate 80 may be or maynot be transparent. Seals 56 and 58 are typically provided to join thesubstrate 100 and backplate 80 to form the fabricated package 51.Depending on embodiments, the seals 56 and 58 may be a non-hermetic,semi-hermetic, or hermetic seal.

In one embodiment, a desiccant 70 is provided within the packagestructure 51 to reduce moisture within the package structure 51. In oneembodiment, the desiccant 70 is positioned between the interferometricmodulator array 54 and the backplate 80. Desiccants may be used forpackages that have either hermetic or semi-hermetic seals. In oneembodiment, the amount of a desiccant used in the interior of thepackage 51 is chosen to absorb the water vapor that permeates throughthe seals 56 and 58 during the lifetime of the device 51.

Throughout the specification, the sampled (or sample) package 51 means apackage which has not been exposed to a humid environment as discussedbelow. Also, throughout the specification, the fabricated package 51means a device which encloses a plurality of interferometric modulators(interferometric modulator array). In certain embodiments, before thehumidity testing, initial measurements (e.g., weight, color, resistance,initial relative humidity, etc.) can be made, if needed (210).

The sampled package 51 is exposed to an environment, for example, via ahumidity chamber 53 that contains sufficient amount of water vapor forthis testing for a certain period of time, e.g., 250-500 hours (220). Inone embodiment, the humidity chamber 53 may provide a more severehumidity condition than an ordinary environment where people actuallylive and use electronics. For example, if the ordinary environment is at40° C. and 90% RH (relative humidity), the humidity chamber 53 can beset, for example, at about 70° C. and 80% RH, or 85° C. and 60%. Thatis, with the use of the humidity chamber 53 for a short period of time,the sampled package 51 can be simulated as if it has been exposed tohumidity much longer than otherwise (e.g., an ambient environment; willbe described).

In another embodiment, the sample package 51 can be exposed to anenvironment (X), other than the humidity chamber 53, where a sufficientamount of humidity exists for this testing or which has a similartemperature humidity level to the humidity chamber 53. In anotherembodiment, the sample package 51 can be exposed to an ambientenvironment (an ordinary environment; Y) where people actually live anduse electronics. In this environment, the exposure time will be longerthan when the sample package 51 is exposed to a more humid environmentsuch as in the humidity chamber 53. Throughout the specification, theterm “a humid environment” may represent at least one of the humiditychamber and the environments X and Y as identified above.

After a certain (predetermined) period of time, the package 51 isremoved from the humidity chamber 53 or other humid environment (230).In one embodiment, depending on the degree of the humidity, the exposuretime can vary. For example, if the sampled package 51 is exposed to amore humid environment such as the humidity chamber 53, thepredetermined period of time will relatively shorter than when thesampled package 51 is exposed to a less humid environment such as anambient environment. For convenience, the package which has been removedfrom the humid environment will be referred to as an exposed package 60.In various embodiments, the humidity testing can be performed for theexposed package 60. In another embodiment, the humidity testing can beperformed for the sample package 51, which has not been exposed to thehumid environment. This testing would be still useful if water vapor hasnot been sufficiently removed from the sample package 51 during thefabrication process. However, for convenience, the humidity testingprocedure will be described with respect to the exposed package 60.

In one embodiment, as outlined in FIG. 8, the humidity testing isperformed based on, for example, a weight measurement testing (A), acolor change of desiccant testing (B), a resistance measurement testing(C), a cold finger measurement testing (D), and the combination of C andD (E). In another embodiment, one or more of the testing processes asindicated above may be combined with each other to provide a number ofhumidity testing processes. In another embodiment, one or more of thetesting processes as indicated above may be modified depending on asituation as exemplified in FIG. 9C (modified version of “A”). In stillanother embodiment, the combination of one or more of the testingprocesses as indicated above may be modified depending on a situation asexemplified in FIG. 10D (modified version of the combination of “A” and“B”).

In various embodiments, the evaluation of the degree of the determinedrelative humidity in the inside of the exposed package 60 may be made byconsidering, for example, at least one of the following parameters: i)temperature-humidity combination (e.g., 40° C. and 90% RH, or 85° C. and60% RH), ii) the thickness and width of the seal 24, iii) adhesivepermeability (e.g., 12.1 gram-mM/m² per day per KPa), iv) desiccantcapacity (e.g., 10% of the desiccant weight), and v) display size (e.g.,1.1 inch diagonal or 4.5 inch diagonal), etc.

FIGS. 9A and 9B illustrate a humidity testing process according to oneembodiment of the invention. In this embodiment, the humidity level ofthe exposed package 60 is determined by comparing the weights of thesample package 51 and the exposed package 60. In another embodiment, thehumidity level in the inside of the exposed package 60 can be determinedby comparing the weight of the exposed package 60 and an average weightof a plurality of sample (unexposed) packages.

Referring to FIG. 9A, the weight of the sample package 51 (i.e. beforethe package is exposed to the humid environment) is measured using aweight measurement device (or scale) 62. In one embodiment, the weightmeasurement device 62 includes any kind of scale which can identify aweight gain. In one embodiment, the weight scale of the device 62 isaccurate to, for example, about ±0.1 mg. In another embodiment, theweight scale of the device 62 is accurate to, for example, about ±0.05mg. In one embodiment, the weight measurement device 62 includes, forexample, AE163 or XS105 available from Mettler.

Referring to FIG. 9B, the weight of the exposed package 60 (i.e. afterthe package is exposed to the humid environment) is measured using theweight measurement device 62. For example, if the weight of the samplepackage 51 is Y (g) and the weight of the exposed package 60 is Y+α (g),the weight gain (α) can be used to evaluate the humidity level in theinside of the exposed package 60. In one embodiment, if the weight gain(α) is greater than a threshold value, the exposed package 60 may bedetermined to be defective or to have a shortened lifetime. For example,for 300 hours of exposure time at 85° C. and 60% relative humidity, theexposed package with about 1 mg weight gain may be determined to bedefective in one test scenario.

FIG. 9C illustrates a humidity testing process according to anotherembodiment of the invention. In this embodiment, the same sampledpackage can be measured at least twice with a predetermined timeinterval. In this embodiment, a sampled package 51 is measured and afirst weight is obtained by the weight measurement device 62. After apredetermined period of time, the sampled package 51 is measured and asecond weight is obtained. As discussed above, the predetermined periodof time varies depending on humidity level requirement. The measuredfirst and second weights are compared. A relative humidity value or adegree of the relative humidity inside the package is determined basedon the weight comparison. In one embodiment, the weight of the sampledpackage 51 is measured more than twice

FIGS. 10A-10C illustrate a humidity testing process according to anotherembodiment of the invention. In this embodiment, the humidity level ofthe exposed package 60 is determined by a color change of the desiccant70 of the exposed package 60. Generally, a desiccant changes its colorwhen it absorbs moisture. Also, generally the color of a desiccant mayvary according to the amount of the moisture that the desiccant hasabsorbed. In one embodiment, a certain desiccant's original color is,for example, blue. In this embodiment, the desiccant 70 may startchanging its color from blue to, for example, red as the desiccantabsorbs moisture around it, for example, at about 25° C. and 15% RH.Furthermore, the desiccant's color may completely turn into a certaincolor (e.g., red) from its original color when the desiccant 70 absorbsmoisture more than a certain amount, at about 25° C. and 40% RH.

In one embodiment, the backplate 80 is made of a transparent material sothat the color change of the desiccant 70 can be seen from the entiretransparent backplate 80. In this embodiment, there is no separatewindow needed to see the desiccant's color or color change. In anotherembodiment, the backplate 80 is neither transparent norsemi-transparent. In this embodiment, the backplate 80 includes atransparent window 72 as shown in FIG. 10A so that the color change ofthe desiccant 70 can be seen from the outside of the package 60 via thewindow 72. In another embodiment, the size of a window 74 may vary asshown in FIG. 10B. In still another embodiment, the backplate 80includes a plurality of transparent windows 76 and 78 as shown in FIG.10C.

In one embodiment, before the sample package 51 is exposed to the humidenvironment, the color of the desiccant 70 can be determined eithermanually or automatically. In this embodiment, the desiccant's color ofthe exposed package 60 can be compared with that of the sample package51 to determine the degree of the color change. After checking the colorof the desiccant 70 of the exposed package 60 and/or comparing thedesiccant's color change between the sampled package 51 and exposedpackage 60, the degree of the detected color and/or the color change maybe used to evaluate the level of the relative humidity in the inside ofthe exposed package 60. In one embodiment, the evaluation comprisescalculating the lifetime of the package and determining whether thesample package 51 is defective or not.

FIG. 10D illustrates a humidity testing process according to anotherembodiment of the invention. In this embodiment, the desiccant 70 doesnot change its color even if it absorbs water vapor. This embodiment isone of destructive humidity testing methods. First, an exposed package60 or a sampled package 51 (hereinafter the exposed package 60) ismeasured by the weight measurement device 62. Secondly, an opening 64 isdefined on an outside portion of the exposed package 60, for example, onthe seal 58 so as to provide water vapor into the package 60. In anotherembodiment, the opening 64 can be defined on another portion, forexample, on the substrate 100, the backplate 80, or the seal 56. In oneembodiment, water vapor may be injected into the package 60 to expeditethe processing with the use of, for example, a pump (not shown). Inanother embodiment, water vapor is allowed to permeate into the package60 without using any device. Next, the exposed package 60 is measuredagain by the weight measurement device 62.

If the desiccant 70 is working properly, it will absorb a significantamount of permeated water vapor during a short period of time, and thesecond weight will be even greater than the first weight. In thissituation, it can be determined that a relative humidity value or adegree of the relative humidity inside the package 60, before definingthe hole 64, was acceptable.

If the desiccant is not working properly, it will not absorb thepermeated water vapor any more, and the second weight will besubstantially the same as the first weight. In this situation, it can bedetermined that a relative humidity value or a degree of the relativehumidity inside the package 60, before defining the hole 64, was quitehigh and not acceptable.

FIGS. 11A and 11B illustrate a humidity testing process according toanother embodiment of the invention. In this embodiment, the relativehumidity in the interior of the exposed package 60 is measured with theuse of a resistive humidity sensor 82. In one embodiment, the sensor 82is connected to a lead 86 of the package 60. The lead 86 can beconnected to an electrode of the interferometric modulator array 54 or aportion of the interferometric modulator array 54, or any interiorportion (for example, on the backplate 80 or the substrate 100) of thepackage 60 where an electrical impedance or resistance can be measuredaround the portion. In one embodiment, the lead 86 is an existing leadof the package 60. In another embodiment, the lead 86 is a patternedlead formed during the interferometric modulator fabrication process forthis humidity testing. In this embodiment, the patterned lead may belocated in an unused portion (e.g., a corner area) of theinterferometric modulator. The patterned lead can be removed ormaintained after the humidity testing is complete. In still anotherembodiment, the lead 86 is a separate lead which can be inserted intothe interior of the package 60 via a hole that is defined for thispurpose.

Generally, the resistance of a material and the relative humidity aroundthe material have an exponential relationship as shown in FIG. 11B. Inone embodiment, the sensor 82 can provide a relative humidity value byconverting the measured resistance value into a corresponding relativehumidity value based on the known relationship between resistance andrelative humidity, e.g., as shown in FIG. 11B.

FIGS. 12A-12C illustrate a humidity testing process according to stillanother embodiment of the invention. In this embodiment, the humiditylevel of the exposed package 60 is determined with the use of a coldfinger device 92. Generally the cold finger device 92 has a hollowportion where refrigerated material (ice, dry ice, etc.) is placed. Inone embodiment, the cold finger device 92 is set at a temperature of,for example, −20° C., −40° C., or −60° C. Alternatively, othertemperatures lower or higher than, or between the exemplifiedtemperatures can be used depending on the embodiment. In one embodiment,the cold finger device 92 is formed of a thermally conductive material,for example, a metal. In one embodiment, certain liquid material such asalcohol can be applied on the contacting area of the cold finger device92 to provide better contact and thermal conductance.

In one embodiment, the cold finger device 92 is configured to contact aparticular area of the backplate 80 as shown in FIG. 12A. In anotherembodiment, the cold finger device 92 is configured to contact aparticular area of the substrate 100 or the seals 56, 58. In stillanother embodiment, the cold finger device 92 is configured to contact aborder area of each seal 56, 58 and the substrate 100. In thisembodiment, frost (will be described below) which has formed in theinterior of the package 60 can be seen via the transparent substrate100.

In one embodiment, the cold finger device 92 is set at a lowtemperature, e.g., −60° C. and makes contact with, e.g., an area 96, asshown in FIG. 12A. It is then determined whether frost has formed in aninside area 94 which corresponds to the contacting area 96. In oneembodiment, whether frost has formed can be visually determined via atransparent window (not shown in FIG. 12A) formed around the contactingarea 96 of the backplate 80. In another embodiment, as discussed above,if the cold finger device 92 makes contact with the substrate 100 or theborder area of the seal 56, 58 and the substrate 100, the tester candetermine via a portion of the transparent substrate 100 whether thefrost has formed in the inside area 94. In still another embodiment, aresistive humidity sensor 82, as discussed with regard to FIG. 11 andshown in FIG. 13, can be used to determine whether frost has formed inthe inside area 94. The embodiment of FIG. 13 is particularly useful todetermine humidity inside the package 60 when the backplate 80 isneither transparent nor includes a transparent portion.

As discussed with respect to FIGS. 11A and 12A, the sensor 82 can beconnected to the lead which is connected to any interior portion of thepackage 60 (for example, the backplate 80 or the substrate 100, etc.)where an electrical impedance or resistance can be measured around theportion. In this embodiment, the cold finger device 92 contacts anoutside area 96 (for example, the backplate 80 or the substrate 100)corresponding to the interior portion. This embodiment is particularlyadvantageous in determining humidity inside the package 60 when at leastone of the backplate 80 and the substrate 100 is not transparent or doesnot include a transparent portion. In one embodiment, if it isdetermined with the cold finger device 92 set at a temperature of, e.g.,−60° C., that no frost has formed in the inside area 94, indicating thatthe interior of the package 60 is sufficiently dry (i.e., havingsufficiently lower humidity) for the intended operation of theinterferometric modulator device, no more humidity testing is generallyrequired. In another embodiment, if it is determined with the coldfinger device 92 set at a temperature of, e.g., −60° C., that frost hasformed in the inside area 94, the humidity testing can be continuedusing a higher temperature (e.g., −40° C.). In this embodiment, if it isdetermined that frost has formed in the inside area 94, either anothertest with a higher temperature (e.g., −30° C.) can be made or no furtherhumidity testing is made according to the embodiment. This test processmay be repeated as many times as desired using different temperaturevalues.

In another embodiment, the cold finger device 92 contacts the substrate100 as shown in FIG. 12B. In this embodiment, frost forms in the area 94inside the package 60. In this embodiment, it is preferable that thebackplate 80 is transparent or includes at least a transparent portionso that the formed frost can be seen via the transparent backplate 80.

In another embodiment, the cold finger device 92 contacts the backplate80 as shown in FIG. 12C. In this embodiment, frost forms in the area 94inside the package 60. In this embodiment, it is preferable that thesubstrate 100 is transparent or includes at least a transparent portionso that the formed frost can be seen via the transparent substrate 100.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the spirit of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers.

1. A method of testing humidity, comprising: measuring i) a first weightof a first device which encloses a plurality of interferometricmodulators and ii) a second weight of a second device which encloses aplurality of interferometric modulators, wherein the first and seconddevices contain a different amount of water vapor; comparing the weightsof the first and second devices; and determining a relative humidityvalue or a degree of the relative humidity inside one of the two devicesbased at least in part upon the weight comparison.
 2. The method ofclaim 1, further comprising: determining the difference between thefirst and second weights; and determining that the device is defectiveor has a shortened lifetime if the difference is greater than athreshold value.
 3. The method of claim 1, wherein the relative humidityvalue or degree is determined considering at least one of the followingparameters: i) temperature-humidity combination inside at least one ofthe devices, ii) the thickness and width of a seal of the at least onedevice, iii) adhesive permeability of a component of the at least onedevice, iv) a desiccant capacity inside the at least one device and v) adevice size.
 4. The method of claim 1, wherein the second deviceincludes a plurality of devices each enclosing a plurality ofinterferometric modulators, at least one of the plurality of devicescontaining a different amount of water vapor from that of the firstdevice, and wherein the second weight is an average weight of theplurality of devices.
 5. The method of claim 1, wherein the seconddevice is the same as the first device, and wherein the measuring of thesecond weight is performed after a predetermined period of time from thefirst weight measurement.
 6. A system for testing humidity, comprising:a first device enclosing a plurality of interferometric modulators; asecond device enclosing a plurality of interferometric modulators,wherein the first and second devices contain a different amount of watervapor; and a scale configured to measure the weights of the first andsecond devices, wherein a relative humidity value or a degree of therelative humidity inside one of the two devices is determined based atleast in part upon the measured weights.
 7. The system of claim 6,wherein the relative humidity value or degree is determined consideringat least one of the following parameters: i) temperature-humiditycombination inside at least one of the devices, ii) the thickness andwidth of a seal of the at least one device, iii) adhesive permeabilityof a component of the at least one device, iv) a desiccant capacityinside the at least one device and v) a device size.
 8. The system ofclaim 6, wherein the scale is accurate to about ±0.1 mg.
 9. The systemof claim 6, wherein the scale is accurate to about ±0.05 mg.
 10. Amethod of testing humidity, comprising: providing a device whichencloses i) a plurality of interferometric modulators and ii) adesiccant; measuring a first weight of the device; providing water vaporinto the inside of the device; measuring a second weight of the deviceafter the water vapor has been provided into the device; comparing thefirst and second weights; and determining a relative humidity value or adegree of the relative humidity inside the device based at least in partupon the weight comparison.
 11. The method of claim 10, wherein thedevice includes a desiccant, and wherein the method further comprisesdetermining that the desiccant is not working properly if the secondweight is substantially the same as the first weight.
 12. The method ofclaim 10 further comprising defining a hole at least one of thefollowing area: a seal, a backplate, and a substrate of the device, andwherein the water vapor is provided into the device via the hole. 13.The method of claim 10, wherein the relative humidity value or degree isdetermined considering at least one of the following parameters: i)temperature-humidity combination inside the device, ii) the thicknessand width of a seal of the device, iii) adhesive permeability of acomponent of the device, iv) a desiccant capacity inside the device andv) a device size.
 14. A system for testing humidity, comprising: meansfor measuring i) a first weight of a first device which encloses aplurality of interferometric modulators and ii) a second weight of asecond device which encloses a plurality of interferometric modulators,wherein the first and second devices contain a different amount of watervapor; means for comparing the weights of the first and second devices;and means for determining a relative humidity value or a degree of therelative humidity inside one of the two devices based at least in partupon the weight comparison.
 15. The system of claim 14, wherein therelative humidity value or degree is determined considering at least oneof the following parameters: i) temperature-humidity combination insideat least one of the devices, ii) the thickness and width of a seal ofthe at least one device, iii) adhesive permeability of a component ofthe at least one device, iv) a desiccant capacity inside the at leastone device and v) a device size.
 16. The system of claim 14, wherein thesecond device includes a plurality of devices each enclosing a pluralityof interferometric modulators, at least one of the plurality of devicescontaining a different amount of water vapor from that of the firstdevice, and wherein the second weight is an average weight of theplurality of devices.
 17. The system of claim 14, wherein the seconddevice is the same as the first device, and wherein the measuring of thesecond weight is performed after a predetermined period of time from thefirst weight measurement.
 18. A system for testing humidity, comprising:means for providing a device which encloses i) a plurality ofinterferometric modulators and ii) a desiccant; means for measuring afirst weight of the device; means for providing water vapor into theinside of the device; means for measuring a second weight of the deviceafter the water vapor has been provided into the device; means forcomparing the first and second weights; and means for determining arelative humidity value or a degree of the relative humidity inside thedevice based at least in part upon the weight comparison.
 19. The systemof claim 18, wherein the device includes a desiccant, and wherein thesystem further comprises means for determining that the desiccant is notworking properly if the second weight is substantially the same as thefirst weight.
 20. The system of claim 18, wherein the relative humidityvalue or degree is determined considering at least one of the followingparameters: i) temperature-humidity combination inside the device, ii)the thickness and width of a seal of the device, iii) adhesivepermeability of a component of the device, iv) a desiccant capacityinside the device and v) a device size.